SEISMICITY IN NORTH-EASTERN BRAZIL - FRACTAL CLUSTERING AND THE EVOLUTION OF THE B-VALUE

We analyse a catalogue of earthquakes recorded near Joao Camara, Brazil, an intraplate area with a simple velocity structure and low attenuation. The evolution of seismicity is characterized by the seismic b value and the fractal dimension of earthquake epicentre locations measured from sliding 100 event windows. The events are divided into a number of spatial clusters using a nearest centroid sorting technique, and two of these clusters are examined in detail. One cluster, characterized by intense activity, shows a clear negative correlation between b value and fractal dimension of epicentre locations, as has been predicted from simple mechanical models. A second cluster shows a weak positive correlation, and it is suggested that this might be explained in terms of fluid flow in the fault zone.